Apparatus for hot-sheathing electric cables with tubular metal sheaths



Jan. 15, 1963 Filed May 11, 1960 P. G. PRIAROGGIA ETAL 3,073,441 APPARATUS FOR HOT-SHEATHING ELECTRIC CABLES WITH TUBULAR METAL SHEATHS 2 Sheets-Sheet 1 lNVENTORS ATTORNEY 6 P. G. PRIAROGGIA ETAL 3,

APPARATUS FOR HOT-SHEATHING ELECTRIC CABLES WITH TUBULAR METAL SHEATHS Filed.May 11, 1960 2 ShSBtS-SIIGBt 2 iNVENTORS,

y r l ATTORNEY United States Patent Ofifice 3,073,441 Patented Jan. 15, 1963 3 073,441 APPARATUS FOR HbT-SHEATHINE ELECTRIC CABLES WITH TUBULAR METAL SHEATHS Paolo Gazzana Priaroggia, Milan, Italy, and Walter ieg fried, Versoix, Geneva, Switzerland, assignors to Plrelll Societa per Azioni, Milan, Italy Filed May 11, 196i), Ser. No. 28,374 7 Claims. (Cl. 207-4) The present invention relates to the extrusion of metal sheaths on electric cables, with particular regard to aluminium sheaths. As is known, in the conventional processes for extruding metal sheaths on electric cables by a ram-type press, the metal is extruded in the solid state and therefore it is necessary to employ very high values of the specific pressure exerted on the metal to impart to it the plastic deformation necessary to secure extrusion. These specific pressures may reach values of thousands of times that of the atmosphere.

The chief object of the present invention is that of operating on the metal as much as possible in the molten state so as to reduce the specific pressures to considerably lower values, the phase of plastic deformation of the metal in the solid state thus being reduced to the indispensable minimum.

In order to im art the necessary pressure to the metal in the liquid state, it is not easy to resort to the usual means, such as the use of rams or the like, first because problems of fluid-tightness where molten metals are concerned require a complicated solution, and secondly since there are other serious problems concerned with the metals used in the construction both of the ram and of the cylinder. In particular, in the case of aluminium, there are practically no steels which are not rapidly corroded by molten aluminium. Moreover the use of rams to transmit pressure is unsuitable for the continuity of the process, unless valve systems are adopted which permit the process to be carried out with a number of cylinders and rams. In any case these methods are very complicated and uncertain in their results.

According to the present invention the use of rams is eliminated and replaced by employing compressed gas, which permits the solution of the problems of fluidtightness and resistance to corrosion of the elements intended to come in contact with molten metal in a considerably simpler way, as will be described below.

in using gas pressure in lieu of a ram, it is necessary to employ gas insoluble in the molten metal to be extruded; in particular, for aluminium, it is very advisable to use argon, which, besides being insoluble in molten aluminium, conveniently protects it from oxidation.

The present invention consists therefore in apparatus for hot-sheathing electric cables with a tubular metal sheath, of the type comprising an extrusion press fed with molten metal, wherein the pressure required for extrusion is supplied by means of compressed gas, fed at the upper end of a substantially vertical press cylinder and that the said cylinder is provided with heating means located immediately upstream of an extrusion nozzle, which is made of a material, at least on its internal surface, resistant to the corrosion of the molten metal and is cooled, in a manner known per se, the heating means serving to tain the metal in the molten state at least up to the extrusion nozzle and the cooling means bringing the metal to the pasty state in proximity to the point of extrusion.

In other words, the invention aims at reducing the work of plastic deformation to the minimum possible by placing the heating and cooling means of the nozzle in such a position as to produce the initial solidification of the metal in the extrusion nozzle but a little before it emerges from the orifice of the said nozzle. If the nozzle comprises only a frusto-conical portion opening at its narrower end directly on to the cable being sheathed, the work of plastic deformation can be considerably reduced but not completely eliminated, as the solidification of the metal preferably takes place only in the downstream portion of the nozzle with respect to the direction of extrth sion. The work of plastic deformation may be practically eliminated by using a nozzle in which the frusto-conical portion terminates in a cylindrical length of uniform diameter; the solidification of the metal takes place in that case when it assumes a cylindrical shape having di- ..ensions nearly equal to those of the extruded sheath, so that all that is then required is the simple operation of drawing the sheath, almost without reducing its diameter. The sheathed cable is drawn through a die and/ or a rolling mill in order to reduce the diameter of the sheath or to stretch it longitudinally so as to impart to it, besides the required size, the necessary flexibility and elasticity.

Although the above-indicated features of the present invention permit elimination of many of the present drawbacks of this technique, they are not suiiicient to overcome the main inconvenience, that is discontinuity of the extrusion operation. This discontinuity is practically due to two main factors, namely, the necessity of supplying the press with molten metal as successive charges in the cylinder are nearly exhausted and frequent interruptions, owing to the replacement of parts in consequence of wear, especially when the molten metal is aluminium, if said parts are constructed according to current practice.

A further aim of the present invention is therefore to provide a form of press cylinder suitable for operation over long periods under all conditions of pressure and with any type of molten metal (in particular aluminium), and also to provide a system for feeding and operating the press capable of securing a continuous output.

In order to comply with these requirements, the cylinder of the press comprises a pressure-resistant outer casing (which may be made of a suitable type of steel), a refractory crucible within the said casing, made of a chemically neutral material with respect to the molten metal, aluminium, and not liable to corrosion by the latter, and a porous or at least gaspermeable layer interposed between the crucible and the casing, this porous layer being subjected to the gas pressure existing in the cylinder so that the gas, penetrating in to the porous material may balance, at least approximately, the pressures acting on the outer and inner surfaces of the crucible. Under these conditions the crucible serves only as a con tainer for the molten metal without being charged with an internal pressure of some tens or hundreds of atmospheres, which is required to extrude the metal.

With regard to the feeding system, the present invention starts from a disposition already known per se in ramtype presses, in which the press cylinder is fed from a melting furnace through an intermediate reserve container. in a previous proposal of this nature, however, the intermediate container served only to feed the press with metal, devoid of oxides and slags, whilst there was no suggestion as to continuous feeding, in particular in the case of molten aluminium. Moreover-and this has considerable importance in evaluating the further scope and value of the present invention-even if in the prior technique it was known to feed an extrusion press with molten metal, such an arrangement served only to ensure adequate continuity between the new molten batch and that nearly exhausted, now in a pasty or even solid state, and it has never been applied practically in the case of molten aluminum by reason of its strong corrosive action on the metals forming the cylinder and the ram of the extrusion press.

According to a further feature of the present invention, continuous extrusion is ensured since the reserve container used is a closed container resistant to internal pressure and provided with means for supplying the gas at an adjustable pressure having a maximum value sufficient to force the molten metal from the container to the press cylinder during extrusion, valves being provided at the inlet and outlet of the reserve container, which are controlled as regards opening and closing by maximumand minimum-level detectors situated in the container and in the press cylinder.

The greatest didrculty in the accomplishment of the above-cited features lies in the construction of the valves which control the intake and output of the molten metal, e.g. aluminium, to and from the reserve container and also in the construction of the container itself. A valve particularly suitable for this purpose is described and illustrated in detail in our co-pending patent application No. 28,373, filed May 11, 1960, now Patent No. 3,052,253,

.ed Sept. 4, 1962.

With regard to the reserve container, it has, according to the invention, a structure similar to that of the cylinder of the extrusion press, in which, between a refractory crucible and its pressure-resistant casing, there is a porous layer, a permeable to the compressed gas fed to the container, so as to equalise the pressures acting on the outer and inner surfaces of the crucible. Moreover, the reserve container is provided with heating devices which, both in the container and in the press, preferably consist of electric windings of resistive and inductive type, embedded in the said porous layer and the supply of electric current to which is controlled by thermo-regulators acting in accordance with the temperature of the molten metal in the container and in the press, respectively.

Further characteristics and advantages of the present invention will appear from the following description, made with reference to the accompanying drawings illustrating by way of example apparatus in accordance therewi h, and in'which:

FZGURE 1 illustrates diagrammatically in vertical section an extrusion press in accordance with the invention;

2 illustrates an alternative form of the extrusion nozzle used in a press as in FIGURE 1, and

FZGURE 3 represents diagrammatically in vertical section a plant for continuous extrusion, employing a press as in FlGURE 1.

Referring to FIGURE 1, the numeral 1 indicates a vertical cylindrical steel casing, resistant to internalpressure, within which a refractory crucible 2 is coaxially disposed. The casing l is closed in a fluid-tight manner by a lid 3 and as shown, the upper edge 2' of the crucible 2 is spaced from the lid 3. Between the crucible 2 and the casing 1 there is a layer of porous material 5, to which atmosphere existing in the crucible 2 has access by vi. .e its spacing from the lid 3. The crucible 2 is preferabl made of graphite which, as known, is not corroded by molten metals. The porous layer 5 may be constituted by any refractory insulating material permeable to gases, as, for instance, a refractory material ground into granules.

All the above-described components form the press cylinder to which the molten aluminium 6 is fed through a steel tubular connection i7, situated in proximity to the upper end of the cylinder and internally lined with tube resistant to the corrosive action of the molten metal, made, for instance, of graphite. A thermometric element 1? extends through the lid 3 and dips into the molten metal 6. The layer 5 contains heating resistors 4 supplied with electric current controlled by the thermome is; element 18 through a known form of thermoregul' tin appliance R, not illustrated in detail in the draworder to maintain the metal 6 constantly in the molten state. I

At the bottom of the casing it there is fixed, in a fluidtight manner, an extrusion head 7 of a type generally lmown for sheathing cables by extrusion, into which extends from the bottom of the crucible 2, a tubular projection '2 designed to feed the head with the molten metal 6. As appears from the figure, the projection 2 is surrounded by a heating resistor in, and a similar resistor 42) surrounds also the neck of the head 7, the resistors id and 45 being controlled in such a way that the metal 6 may enter in the molten state into an annular trusto-conical passage "7a in the head 7'. This passage becomes narrower in the direction of extrusion P and op'ns directly on to the cable 8 to be sheathed.

.e passage 7a is cooled from outside and from inside by means of jackets 7b, 7c, fed with a cooling fluid through ducts and for the former and through similar ducts, not shown in the figure, for the latter.

in this way solidification of the metal takes place near the outlet of the annular passage 7a, whilst in proximity to the inlet it is still in the liquid state, although very near to the solidification point, so that it is important to protect he inn r surface of that passage from the corrosive action the metal. For this purpose the nozzle 70 may be made entir ly of metal not liable to corrosion by the molten metal, for instance, titanium, but it may be advisable to make it of steel or other metal and to line it either with a non-corrodible metal or with a suitable corrosion-resistant enamel, for instance, chromium boride or aluminium oxide or other like material which may be applied by spraying or other method.

"5 he cylinder of the press is provided with maximumminimum-level detectors, i5, 14, which function when the molten metal 6 reaches the respective levels, so that the supply of molten metal may be stopped or fed to the press through the connection 16, 17.

The lid 3 is fitted with a pipe 1?, controlled by a valve 29a, for admitting compressed gas, for instance argon, into the cylinder. The pipe i9 is moreover provided with an exhaust valve 2%, through which the gas may be discharged from the press and, if desired, recovered.

Supposing that the press is in the above-described condition and that the connection re, 17 is closed in a fluidtight manner by means of a suitable valve, the valve it) is closed and the valve 19:! is opened so as to feed compressed gas to the cylinder of the press. At the same time the cable 8 is advanced through the head 7 in the direction of the arrow F and the heating and cooling means 4, 3a, 4b, 7b, 7c are adjusted in such a way as to cause the solidification to the pasty stage of the metal r5 only within the downstream portion of the passage 7a, this portion being indicated at A. The work of extrusion is therefore substantially reduced to the extrusion of the solid metal, still easily deformable by virtue of its high temperature, existing in proximity to the extrusion point. The tubular metallic sheath 21 so produced on the cable 3 is rapidly cooled at its exit from the extrusion nozzle by means of water jets ii. in consequence of the limited degree of plastic deformation suffered by the solid metal in the extrusion head the resulting sheath 21 will be nearly always less flexible and elastic than is desired. Consequently it will be advisable to impart to the sheath the necessary mechanical properties by subjecting it to a degree of cold-working, such as by drawing the whole through a die 12 and/or a rolling mill 13.

When the stock of molten metal 6 in the press falls to the level of the detector 1 3, the valve 19a situated in the duct 19 is closed and the exhaust valve 20 is opened; then a new amount of molten metal is supplied through the connection re, 17 up to the maximum level, indicated by the detector 15, and the above-described cycle is repeated. In this mode of operation the extrusion process is discontinuous.

Alternatively, the supply of the molten metal could be tried out without releasing the press from the extrusion essure, namely, without clot .1; the valve and open ing the valve 20. This continuous process will be hereafter described with reference to FIGURE 3.

The extrusion head illustrated in FIGURE 2 has the object of substantially reducing the extrusion pressure by eliminating the work of plastic deformation of the solid metal. For this purpose the extrusion nozzle 7a is made of a material which, at least on its internal surface, is resistant to the corrosive action of the molten metal and comprises a convergent portion B and a cylindrical portion C of constant diameter. The portion B is provided With additional heating resistors 4c and 4d, while the cooling interspaces 7b and 70 extend practically only along the length of portion C. The portion B is therefore traversed by the metal still in the molten state, solidification occurring only in the portion C of constant diameter. Owing to the existence of the cooling interspace 70 between the cable 8 and the metal flowing through portion C, the resulting sheath 21 has an inner diameter somewhat greater than the outer diameter of the cable. Moreover, on account of the practically negligible degree of plastic deformation, the sheath 21' is relatively brittle. In this case it is therefore necessary to resort to a subsequent cold mechanical working of the sheath by means of reduction units, analogous to those indicated at 12 and 13 in FIGURE 1, which stretch the sheath 21 and reduce its diameter so as to bring it into contact With the cable 8.

In the apparatus depicted in FIGURE 3 a single reference P indicates the press already described with reference to FIGURE 1, essential details of the press itself being designated by the same reference numerals as are used above.

The press P is fed with molten metal, e.g. aluminium, supplied from a melting furnace Q through a reserve container S, the elements Q, S and P being preferably disposed in cascade fashion so that the weight of the molten metal assists its conveyance from Q to P.

The structure of the container S is substantially identical with that of the press cylinder P: thus the container S has an outer pressure-resistant steel casing 101, with a fluid-tight lid 103. The casing contains a graphite crucible 1G2, whose upper end is spaced below a lid 103 in such a way that a porous layer 195, interposed between the crucible and the casing, is exposed to the atmosphere existing in the crucible in order to balance the pressures. The layer 165 contains heating resistors 104, and minimumand maximum-level detectors 114, 115 respectively are fitted to provide indication of the corresponding levels. A thermometric element 113 extends through the lid 163 into the molten metal 6' contained in the crucible 1G2, and compressed gas is supplied to the container through a pipe 19 fitted in the lid 193 and provided with a cutoff valve 119a and an exhaust valve 129. The connection 16, 17, carrying the molten metal to the pr ss P, is located at the bottom of the crucible.

The melting furnace Q comprises a steel casing 2%, containing a graphite crucible 202, surrounded by heating resistors 204 embedded in an intermediate thermoinsulating layer 2%, which may be made of the material used for the layers 105 and 5 in the container S and in the press P. The furnace is of the open-top type and is fed with aluminium ingots to obtain the molten metal 6".

A tubular connection 117, with an inner graphite lining 1116, leads from the bottom of the furnace Q to the upper end of the container S, similarly to the connection 17 to the upper end of the :press P.

The connections 17 and 117 are respectively controlled by valves 22 and 122, each comprising a throttled passage for the molten metal which, as in the nozzle 71!, is made of a material which, at least on its internal surface, is resistant to the corrosive action of the molten metal and is surrounded by a cooling jacket which is in turn surrounded by an inductive heating winding 23 or 123 respectively. A valve of this type is described and illustrated in the above-cited co-pending patent application 6 No. 28,373, filed May 11, 1960, now Patent No. 3,052,- 253, issued September 4, 1962.

The winding 23 of the valve 22 is supplied by a generator G connection of which thereto is controlled by the minimum-level detector 14 of the press P. Similarly, the winding 123 of the valve 122 is supplied by a generator G, whereof connection is controlled by the minimum-level detector 114 of the container S. Timing devices T and T are associated with the generators G and G in order to disconnect the corresponding generator after a predetermined time, adjustable at will and determined by the maximum time required for the melting of the metallic plug formed in the respective valves 22 and 122 in the preceding cooling phase.

According to an alternative arrangement, the timing devices T and T could be dispensed with, having the connection and disconnection of the generators G and G to the corresponding minimum-level detectors 114 and 14. S0, for instance, making reference to the detector 14, the generator G would be connected as soon as the level of the metal 6 drops below the detector, so that the plug of solid metal in the valve 22 would be fused shortly afterwards; the resultant flow of molten metal from the container S to the press P will then raise the level of the metal 6 in the latter, thus submerging at a predetermined moment the minimum-level detector 14 which, being again immersed in the metal, disconnects the generator G The generator G with its detector 114 would be operated in the same Way.

This double effect of the detectors may, moreover, be applied to the detectors 1S and 1.15 for the connection and disconnection of the cooling circuits of the valves 22 and 122. In fact, for instance in the case of detector 15, it inserts the cooling circuit as soon as it is reached by the level of the metal 6 supplied to the press; however, as the solidification of the metal in the valve 22 is not instantaneous, the metal will continue to be fed to the press for a certain time, in spite of the action of the detector 15; ultimately its supply is stopped, Whilst its output is continued through the extrusion head. Hence, at a predetermined moment, the detector 15 will emerge from the metal 6 and will disconnect the cooling circuit of the valve 22, saving the power consumption and preventing the cooling effect from acting on the metal contained in the connection 17 outside the valve 22.

The heating elements 4, 4a and 184, of the press P and of the container S are controlled by the corresponding thermometric elements 13 and 118, through regulators R and R, respectively, in order to maintain the metal always in the molten state. Also the connections 17 and 117 may be provided with heating elements on those portions outside the corresponding valves 22 and 122.

A thermal control system will be similarly provided for the extrusion head 7, in order to adjust both the heating elements 4b, 4c, 4d and the cooling elements 7b, 70, disposed therein so as to ensure the solidifiication of the metal in the desired zone.

In order to operate the above-described apparatus continuously, the procedure is as follows:

Assuming that the valves 22 and 122 are closed by plugs of solid metal and that the press P, the container S and the furnace Q contain molten aluminium as illustrated, extrusion pressure is applied to the press P through the duct 19 to carry out extrusion in the manner already described with reference to FIGURE 1. When the molten metal 6 reaches the minimum level, the detector 14 connects the generator G which excites the winding 23, so causing the plug of solid metal filling the throttled passage in the valve 22 to melt. The same detector also acts to open the valve 11911 for the inlet of compressed gas to the container S.

The gas fed to the container S must be at least at the same pressure as that fed to the press P; if necessary, the pressure in S will be higher than that in P, even if '7 the transfer of molten metal is favoured by the head of the metal 6' in the container S, so as to carry out a relatively expeditious transfer. 7

The transfer begins as soon as the solid plug in the valve 22 has melted; then the generator G is disconnected by means of its timing device. The amount of molten metal supplied to the press is determined by the detector of the press. As soon as the level of the metal 6 has reached its maximum, the detector 15 operates to balance the pressures acting on the two ends of the connection 17 and to send cooling fluid to the jacket of the valve 22. In this way the amount of molten metal which is now stationary in the neighborhood of the valve is solidified, thus forming the solid closing plug of the valve which precludes any flow between S and P. The

press P has thus been supplied with molten metal without interrupting the extrusion process.

The serviceable volume of the container S should be at least equal to that of the press cylinder. If needed, two or more containers 8 may be provided, in parallel between the furnace Q and the press P.

When the level of the molten metal 6' in the container 7 drops to the predetermined minimum, the detector 114 connects the generator G and opens the exhaust valve 12d, thus putting the inside of the container S at atmospheric pressure. The valve 122 operates in the manner already described with respect to the valve 22, so that the molten metal 6" is transferred from the furnace Q to the container S. When the level of the metal 6' in the container reaches the predetermined maximum, the detector 115 operates to balance the pressures acting on the opposite ends of the connection 117 and to send cooling fluid to the jacket of the valve 122 to form a solid cut-off plug. The furnace Q is fed in a way already known with aluminium ingots, as above stated.

As the molten metal is always drawn from the bottom 'of the furnace Q and of the container S, and as the comjpressed gas, preferably argon, is insoluble in molten aluminium and is chemically neutral, the metal reaches the press P in the purest condition, so that the sheath extru-ded on to the cable is devoid of faults.

if desired, also the furnace Q could work in an argon atmosphere, by providing it with a gas-tight cover and with gas feeding means similar to 19, 19a and 20.

The control circuit between the detectors l5 and 115 and the devices controlled by them have not been illustrated or described in detail in the present specification, being widely known and available on the market. They are merely electric remotecontrol devices, operated by their corresponding detectors and operating valves or switches for the changing over or regulation of the compressed gas as well as of the cooling fluid for the valves 22. and 122. For the same reason the thermo-regulators R, R and the generators G, G have not been described in detail. With regard to these latter, it is suficient to add that the frequencies used to melt the solid plug in the valves 22 and 122 lie in the range between 500 and 500,600 cycles per second, and that the generators are so rated as to carry out the required fusion, at the most, within a few seconds.

The two generators could be replaced by a single generator, selectively connectible to the valves 22 and 122 controlled by the detectors l4 and 114.

What we claim and desire to secure by Letters Patent in the United States is:

1. Apparatus for hot-sheathing electric cables with a tubular metal sheath consisting of an extrusion press compnsing in combination a substantially vertical press cylinder built up of an outer casing resistant tointernal pressure, means supplying compressed gas to said cylinder, a

refractory crucible within the said casing, and a porous layer consisting of refractory material ground into granporous layer being subjected to the pressure of the gas in the crucible so as to approximately balance the pressures acting on the outer and inner surfaces of the crucible, heating means operative to maintain extrusion metal within said cylinder in a molten condition, means for introducing gas under pressure into the upper part of said cylinder, an extrusion nozzle in communication with said cylinder and means for the circulation of a cooling me dium in operative relationship with said nozzle.

2. Apparatus according to claim 1, in which the press cylinder is supplied from a melting furnace through a reserve container, characterized by the fact that the said reserve container is constituted by a closed casing, resistant to internal pressure and provided with gas-supplying means at an adjustable pressure having a maximum value sufficient to force the molten metal from the con tainer to the press cylinder during the extrusion process, valves, made, at least on their internal surfaces, of a material resistant to corrosion by the molten metal, being provided at the inlet and outlet of the reserve container, these valves being respectively controlled for closing and opening by minimumand maximum-level detectors located correspondingly in the container and in the press cylinder.

3. Apparatus according to claim 1, in which the extrusion nozzle comprises a convergent portion followed, in the direction of movement of the cable, by a cylindrical portion, characterized by the fact that the convergent portion is provided with heating means to prevent the solidiication of the metals in said portion, while the cylindrical portion is provided with cooling means to ensure the solidification of the metal in this portion.

4. Apparatus according to claim 1, in which the press cylinder is supplied from a melting furnace through a reserve container, characterized by the fact that the said reserve container is constituted by a closed casing, resistant to internal pressure and provided with gas-supplying means at an adjustable pressure having a maximum value sufficient to force the molten metal from the container to the press cylinder during the extrusion process, valves, made, at least on their internal surfaces, of a material resistant to corrosion by the molten metal, being provided at the inlet and outlet of the reserve'container, these valves being respectively controlled for closing and opening by minimumand maximum-level detectors located correspondingly in the container and in the press cylinder, said reserve container comprising an outer casing resistant to internal pressure, a refractory crucible in the said casing and a layer of porous material interposed between the crucible and the casing, the said porous layer being subjected to the pressure existing in the container so as approximately to balance the pressures acting on the outer and inner surfaces of the crucible.

5. Apparatus according to claim 1, in which the press cylinder is supplied from a melting furnace through a reserve container, characterized by the fact that the said reserve container is constituted by a'closed casing, resistant to internal pressure and provided with gas-supplying means at an adjustable pressure having a maximum value sufficient to force the molten metal from the container to the press cylinder during the extrusion process, valves, made, at least on their internal surfaces, of a material resistant to corrosion by the molten metal, being provided at the inlet and outlet of the reserve container, these valves being respectively controlled for closing and opening by minimumand maximum-level detectors located correspondingly in the container and in the press cylinder, said reserve container comprising an outer casing resistant to internal pressure, a refractory crucible in the said casing and a layer of porous material interposed between the crucible and the casing, the said porous layer being subjected to the pressure existing in the container so as approximately to balance the pressures acting on the outer and inner surfaces of the crucible, heating means surrounding the crucible of the reserve conove r41 tainer, thermometric elements respectively located in said press cylinder and said reserve container, and thermoregulators operatively connected to said thermometric elements and in controlling connection with said heating means of said press cylinder and said reserve container, respectively.

6. Apparatus according to claim 1, in which the press cylinder is supplied from a melting furnace through a reserve cont; 'ner, characterized by the fact that the said reserve container is constituted by a closed casing, resistant to internal pressure and provided with gas-supp1ying means at an adjustable pressure having a maximum value sufficient to force the moltenrnetal from the container to the press cylinder during the extrusion process, valves, made, at least on their internal surfaces, of a material resistant to corrosion by the molten metal, being provided at the inlet and outlet of the reserve container, these valves being respectively controlled for closing and opening by minimumand maximum-level detectors lo cated correspondingly in the container and in the press cylinder, said valves being so constructed as to be closed by the solidification of the molten metal, an inductive heating winding for each valve, electric generators operatively connected to said heating windings respectively, controlling connections from said minimum-level detectors to said respective generators, and cooling means for each of said valves, said cooling means being respectively controlled by said maximunrlevel detectors.

7. Apparatus according to claim 1, in which the press cylinder is supplied from a melting furnace through a reserve container, characterized by the fact that the said reserve container is constituted by a closed casing, resistant to internal pressure and provided with gas-supplying means at an adjustable pressure having a maximum value suiiicient to force the molten metal from the container to tne press cylinder during the extrusion process, valves, made, at least on their internal surfaces, of a material resistant to corrosion by the molten metal, being provided at the inlet and outlet of the reserve container, these valves being respectively controlled for closing and opening by minimurnand maximum-level detectors located correspondingly in the container and in the press cylinder, said valves being so constructed as to be closed by the solidification of the molten metal, an inductive heating winding for each valve, electric generators operatively connected to said heating windings respectively, controlling connections from said minimum-level detec tors to said respective generators, cooling means for each or" valves, said cooling means being respectively controlled by said maximum-level detectors, timing devices respectively associated with said generators, whereby each generator is disconnected from its associated heating winding at a predetermined and adjustable time after its connection thereto by the corresponding maximum level detector.

References Cited in the file of this patent UNlTED STATES lTATENTS 

1. APPARATUS FOR HOT-SHEATHING ELECTRIC CABLES WITH A TUBULAR METAL SHEATH CONSISTING OF AN EXTRUSION PRESS COMPRISING IN COMBINATION A SUBSTANTIALLY VERTICAL PRESS CYLINDER BUILT UP OF AN OUTER CASING RESISTANT TO INTERNAL PRESSURE, MEANS SUPPLYING COMPRESSED GAS TO SAID CYLINDER, A REFRACTORY CRUCIBLE WITHIN THE SAID CASING, AND A POROUS LAYER CONSISTING OF REFRACTORY MATERIAL GROUND INTO GRANULES INTERPOSED BETWEEN THE CRUCIBLE AND THE CASING AND IN CONTACT WITH THE OUTER SURFACE OF THE CRUCIBLE, THE SAID POROUS LAYER BEING SUBJECTED TO THE PRESSURE OF THE GAS IN THE CRUCIBLE SO AS TO APPROXIMATELY BALANCE THE PRESSURES ACTING ON THE OUTER AND INNER SURFACES OF THE CRUCIBLE, HEATING MEANS OPERATIVE TO MAINTAIN EXTRUSION METAL WITHIN SAID CYLINDER IN A MOLTEN CONDITION, MEANS FOR INTRODUCING GAS UNDER PRESSURE INTO THE UPPER PART OF SAID CYLINDER, AND EXTRUSION NOZZLE IN COMMUNICATION WITH SAID CYLINDER AND MEANS FOR THE CIRCULATION OF A COOLING MEDIUM IN OPERATIVE RELATIONSHIP WITH SAID NOZZLE. 